Method for fluxing molten-metal

Abstract

An improved method for dispersing high levels of fluxing gas in a body of molten aluminum using an impeller or disperser to disperse the fluxing gas in the body of molten aluminum, the method producing increased shear forces in the body of molten aluminum and reducing vortex formation. The method comprises the steps of providing a body of molten aluminum and a disperser in the body. A fluxing gas is added to the body at the rate of 1 to greater than 200 SCF/hour and dispersed by rotating the disperser in one direction and thereafter reversing the direction of rotation to a counter direction. The direction of rotation is reversed periodically to substantially reduce formation of a vortex and to provide increased shear forces in the body for purposes of improving dispersion of the fluxing gas in the molten aluminum.

What is claimed is: 
     
       1. An improved method for fluxing a body of molten aluminum using a disperser to disperse fluxing gas in the body of molten aluminum, the method producing increased shear forces in the body of molten aluminum and reducing vortex formation, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing a disperser in said body;   (c) adding fluxing gas to said body, said fluxing gas being provided at a rate in the range of 1 to greater than 650 SCF/hour; and   (d) dispersing said fluxing gas in said body by: (i) rotating said disperser in one direction; and thereafter   (ii) reversing the direction of rotation of said disperser to a counter direction;   (iii) the direction of rotation of said disperser being reversed periodically to substantially reduce formation of a vortex and to provide increased shear forces in said body for purposes of improving treatment of said molten aluminum by improved dispersion of said fluxing gas therein.     
     
     
       2. The method in accordance with claim 1 wherein the fluxing gas is introduced at a rate of 5 to 425 SCF/hour. 
     
     
       3. The method in accordance with claim 1 wherein the fluxing gas is introduced at a rate of 10 to 250 SCF/hour. 
     
     
       4. The method in accordance with claim 1 wherein the fluxing gas is introduced through a shaft on which said disperser is mounted. 
     
     
       5. The method in accordance with claim 1 wherein the fluxing gas is introduced to said body adjacent said disperser. 
     
     
       6. The method in accordance with claim 1 wherein the fluxing gas is comprised of Cl 2  and SF 6  in a ratio in the range of 2:1 to 10:1 parts Cl 2  to SF 6 . 
     
     
       7. The method in accordance with claim 1 wherein the direction of rotation of said disperser is reversed at least every 10 minutes. 
     
     
       8. The method in accordance with claim 1 wherein the direction of rotation of said disperser is reversed at least every 3 minutes. 
     
     
       9. The method in accordance with claim 1 wherein the direction of rotation of said disperser is reversed in a time period in the range of 0.1 seconds to 4 minutes. 
     
     
       10. An improved method for dispersing a fluxing gas in a body of molten aluminum using a disperser to disperse the fluxing gas in the body of molten aluminum, the method producing increased shear forces in the body of molten aluminum and reducing vortex formation, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing a disperser in said body;   (c) adding fluxing gas to said body at a rate in the range of 5 to 425 SCF/hour, the fluxing gas comprised of Cl 2  and SF 6  in a ratio in the range of 2:1 to 10:1 parts Cl 2  to SF 6  ; and   (d) dispersing said fluxing gas by: (i) rotating said disperser in one direction; and thereafter   (ii) reversing the direction of rotation of said disperser to a counter direction;   (iii) the direction of rotation of said disperser being reversed periodically to substantially reduce formation of a vortex and to provide increased shear forces in said body for purposes of improving treatment of said molten aluminum by improved dispersion of said fluxing gas therein.     
     
     
       11. An improved method for dispersing a fluxing gas in a body of molten aluminum using an impeller to disperse the fluxing gas in the body of molten aluminum, the method producing increased shear forces in the body of molten aluminum and reducing vortex formation, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing an impeller on a shaft in said body;   (c) adding fluxing gas to said body by one of passing said fluxing gas through said shaft and adding said fluxing gas adjacent said impeller, the fluxing gas being added at a rate in the range of 5 to greater than 250 SCF/hour; and   (d) dispersing said fluxing gas by: (i) rotating said impeller in one direction; and thereafter   (ii) reversing the direction of rotation of said impeller to a counter direction;   (iii) the direction of rotation of said impeller being reversed periodically to substantially reduce formation of a vortex around the shaft of said impeller and to provide increased shear forces in said body for purposes of improving fluxing of said molten aluminum by improved dispersion of said fluxing gas therein.     
     
     
       12. The method in accordance with claim 10 wherein the direction of rotation of said impeller is reversed at least every 10 minutes. 
     
     
       13. The method in accordance with claim 10 wherein the direction of rotation of said impeller is reversed at least every 3 minutes. 
     
     
       14. The method in accordance with claim 11 wherein flow of fluxing gas to the body of molten aluminum is interrupted when the impeller is reversing direction of rotation. 
     
     
       15. An improved method for dispersing a fluxing gas in a body of molten aluminum using a impeller to disperse the fluxing gas in the body of molten aluminum, the method producing increased shear forces in the body of molten aluminum and reducing vortex formation, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing a impeller on a hollow shaft in said body;   (c) adding treatment fluxing gas to said body by passing said fluxing gas through said shaft at a rate in the range of 5 to 50 SCF/hour; and   (d) dispersing said fluxing gas by: (i) rotating said impeller in one direction; and thereafter   (ii) reversing the direction of rotation of said impeller to a counter direction;   (iii) the direction of rotation of said impeller being reversed every 0.1 seconds to 5 minutes to substantially reduce formation of a vortex around the shaft of said impeller and to provide increased shear forces in said body for purposes of improving treatment of said molten aluminum by improved dispersion of said fluxing gas therein.     
     
     
       16. The method in accordance with claim 15 wherein rotational speed of said body of molten metal is maintained at 0.01 to 70 percent of the rotational speed of said impeller after reversing of rotation direction. 
     
     
       17. The method in accordance with claim 15 wherein the fluxing gas is selected from inert gases, nitrogen containing gases, carbon containing gases and halogen gases and combinations thereof. 
     
     
       18. The method in accordance with claim 15 wherein the fluxing gas is selected from nitrogen, argon, chlorine, sulfur hexafluoride, carbon monoxide and fluorine and combinations thereof. 
     
     
       19. The method in accordance with claim 15 wherein the fluxing gas is comprised of Cl 2  and SF 6  wherein the Cl 2  and SF 6  are maintained in a ratio in the range of 2:1 to 10:1 parts Cl 2  to SF 6 . 
     
     
       20. A method for producing increased shear forces in a body of molten aluminum by movement of the molten metal within the body, the movement providing improved dispersion of a fluxing gas within the body, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing a mixing means for applying movement to said body;   (c) adding fluxing gas to said body at a rate in the range of 1 to 425 SCF/hour; and   (d) creating said shear forces by: (i) applying said mixing means in one direction; and thereafter   (ii) reversing the direction of applying said mixing means to a counter direction;   (iii) the direction of applying said mixing means being reversed periodically to provide said increased shear forces in said body for purposes of improving dispersion of said fluxing gas therein.     
     
     
       21. A method for producing increased shear forces in a body of molten aluminum by inducing movement of portions of the molten aluminum in different directions within the body, the movement providing improved dispersion of a fluxing gas within the body, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing a mixing means for applying movement to said body;   (c) adding a fluxing gas comprised of Cl 2  and SF 6  in a ratio in the range of 2:1 to 10:1 parts Cl 2  to SF 6  to said body at a rate in the range of 1 to 200 SCF/hour; and   (d) creating shear forces by: (i) moving portions of said molten aluminum in one direction by applying said mixing means in one direction; and thereafter   (ii) moving portions of said molten aluminum in another direction by changing the direction of applying said mixing means;   (iii) the direction of applying said mixing means being changed periodically to provide said increased shear forces in said body for purposes of improving dispersion of said fluxing gas therein.     
     
     
       22. The method in accordance with claim 20 wherein the fluxing gas is introduced at a rate of 5 to 50 SCF/hour. 
     
     
       23. The method in accordance with claim 20 wherein the fluxing gas is introduced at a rate of 10 to 25 SCF/hour. 
     
     
       24. An improved method for dispersing a fluxing gas in a body of molten aluminum using an agitator to disperse the fluxing gas in the body of molten aluminum, the body having a top surface, the method producing sub-surface turbulent mixing and increased shear forces in the body of molten aluminum while maintaining the top surface substantially free of vorticity, the method comprising the steps of: (a) providing a body of molten aluminum;   (b) providing an agitator in said body;   (c) adding fluxing gas to said body at a rate in the range of 1 to 200 SCF/hour;   (d) dispersing said fluxing gas by: (i) rotating said agitator in one direction; and thereafter   (ii) reversing the direction of rotation of said agitator to a counter direction;   (iii) the direction of rotation of said agitator being reversed periodically to produce sub-surface turbulent mixing and to increase shear forces in said body while maintaining the top surface substantially free of vorticity for purposes of minimizing skim ingestion during treatment of said molten metal with fluxing gas.     
     
     
       25. The method in accordance with claim 24 wherein the fluxing gas is comprised of Cl 2  and SF 6  in a ratio in the range of 2:1 to 10:1 parts Cl 2  to SF 6 .